High coercivity, cobalt-doped ferrimagnetic iron oxide particulates

Abstract

Highly coercive, cobalt-doped ferrimagnetic iron oxide particulates comprised of ferrous iron and well-adapted for the manufacture of various magnetic recording media, are prepared by (i) thermally decomposing a β-diketone/cobalt complex onto fluidized iron oxide particles having the formula (FeO) x Fe 2 O 3 , wherein 0≦x≦1.5, (ii) next annealing the particulates which result at a temperature ranging from about 300° to 500° and then (iii) permitting the same to cool, while at the same time sweeping the cooling zone with an inert gas, and then (iv) controlledly re-oxidizing the annealed/cooled particles.

What is claimed is: 
     
       1. A process for the preparation of high coercivity, cobalt-doped ferrimagnetic iron oxide particulates, said particulates comprising ferrous iron, and which process comprises (i) thermally decomposing a β-diketone complex of cobalt having a decomposition temperature in the range of 300° to 500° C., and a sublimation point therebelow, onto fluidized iron oxide particles having the formula (FeO) x  Fe 2  O 3 , wherein 0≦x≦1.5, (ii) next, in an inert atmosphere, annealing the particulates which result at a temperature ranging from about 300° to 500° C. and then (iii) permitting the same to cool, while at the same time sweeping the cooling zone with an inert gas, and thence (iv) controllably re-oxidizing the annealed, cooled particles to effect formation of cobalt ferrite thereon, the cobalt being present in the form of Co +2 . 
     
     
       2. The process as defined by claim 1, said β-diketone complex of cobalt having the formula, Co(L) n , wherein n is 2 or 3, and L has the formula: ##STR5## in which R 1  and R 2  are lower alkyl. 
     
     
       3. The process as defined by claim 2, said complex being cobalt acetylacetonate. 
     
     
       4. The process as defined by claim 2, said complex being Co(thd) 3  or Co(thd) 2 . 
     
     
       5. The process as defined by claim 1, said iron oxide particles having the formula (FeO) x  Fe 2  O 3  having been prepared via dehydration and reduction of acicular particles of iron oxide-hydroxide. 
     
     
       6. The process as defined by claim 1, said iron oxide particles being fluidized in a carrier gas consisting of a mixture of nitrogen and hydrogen, and said cobalt complex being sublimed therein. 
     
     
       7. The process as defined by claim 1, wherein the controllable re-oxidation is effected with a mixture of air and inert gas at a temperature ranging from 200° to 300° C. 
     
     
       8. The process as defined by claim 1, the annealed particulates being cooled in step (iii) to ambient temperature.